The present invention relates to a circulating fluidized bed reactor and a convertible combustion method applicable thereto.
The development of new regulations limiting greenhouse gas emissions, including carbon dioxide in fossil fuel power plants, is leading to the implementation of technologies for capturing the carbon dioxide present in the flue gases that are produced as a result of the combustion of fuel in the presence of air.
The technology frequently used to capture carbon dioxide consists of scrubbing the flue gases that have been diluted with nitrogen from the air employed for combustion purposes using solvents, which absorb the carbon dioxide and then restore the carbon dioxide as a concentrated carbon dioxide gas stream after the solvent has been regenerated by the heating thereof.
Such technology for its implementation consumes considerable energy and substantially decreases the efficiency of the fossil fuel power plants where such technology is utilizes, that is, decreases the efficiency of such fossil fuel power plants by more than fifteen percentage points.
U.S. Pat. Nos. 4,498,289 and 5,175,995 teach the use of oxygen as an oxidizer instead of air in boilers wherein steam is produced.
The advantage of using oxygen rather than air as an oxidizer is the reduction, going as far as the complete removal thereof, of the nitrogen, which is employed for purposes of diluting the carbon dioxide present in the flue gases and which originates from the nitrogen present in the air employed for combustion purposes as well as the substantial reduction in the size of the equipment required for such a purpose, thereby resulting in a flue gas flow rate that is approximately 35%-40% of the typical flue gas flow rate when air is employed for combustion purposes.
The application of this principle to a circulating fluidized bed boiler is disclosed in patent U.S. Pat. No. 6,505,567. According to the teachings of this document, a steam generator having a fluidized bed furnace includes means for introducing substantially pure oxygen into said steam generator.
The advantage of such a circulating fluidized bed technique is alleged to be that it permits the extraction of the heat in the circulating solids loop and the maintenance of a low combustion temperature, independently of the oxygen content of the oxidizer that is being utilized for combustion purposes. Hence such a technique is particularly attractive and serves to maximize the amount of oxygen in the oxidizer that is being utilized for combustion purposes, while at the same time minimizing the size of the circulating fluidized bed boiler, the size thereof being dependent directly on the flow rate of the flue gases that are produced during combustion.
However, according to this prior art, there are no teachings of any means that would be capable of being employed for purposes of effectively converting a circulating fluidized bed reactor, which is designed to utilize air for combustion purposes into a circulating fluidized bed reactor that is capable of utilizing oxygen for combustion purposes.